Method of making copper phosphate



Patented 15, 1939 UNITED STATES PATENT orric 2,169,576 I METHOD or MAKINcorral; PHOSPHATE Charles Booth and Herbert J. Krase, Anniston,

Ala, assignors, by mesne assignments, to Monsanto Chemical Company, acorporation of Delaware No Drawing. Application June 18,1936,

' Serial No. 85,886

5 Claims.

This invention relates to a copper containing fungicide-and method ofmaking the same.

One' of the objects of thepresent invention is the provision of aprocess for making a copper phosphate fungicide by electrolyticdissolution of metallic copper. A further object is the provision ofasafe and efficient fungicide.

We have found that if a copper anode, together with a cathode madeeither of copper or an inert material be immersed in a solutioncontaining sodium phosphate and sodium sulfate and a suitable directcurrent be passed through said electrodes, that a copperphosphate-sodium phosphate complex will be precipitated. in theelectrolyte invery finely divided form. This operation may be madecontinuous by continuously removing the precipitated copper-sodiumphosphate complex from the solution and-continuously replenishing theelectrolyte. According to our invention it is possible to operatethecell without diaphragms, thus simplifying the operation con-' siderably.v In previous work on the production of copper phosphate by electrolysisof copper anodes it has been proposed to utilize an electrolytecontaining chlorine compounds, particularly sodium perchlorate (GermanPatent 91,707). Furthermoreit has, hitherto been found necessary toutilize diaphragms surrounding the cathode. For continuous production bythe electrolytic methodwe have found that chlorine compounds areundesirable in the electrolyte, particularly when preparing copperphosphate since the presence of such compounds causes the formation of alayer or coating over the anodes which in time increases the-resistanceof the cell. The use of chlorate in the electrolyte in a short timebuilds and relatively high efliciencies obtained. For

reasons already stated it is desirable that the chlorine content of theelectrolyte either as chlorine ion or as chlorate ion be relatively low.By way of example we give the following description of one method ofcrryinz out'our in-'- vention:

An electrolytic cell having copper anodes and cathodes is connected to asuitable source of direct current. The current density used may bevaried between 15 and amperes per sq. ft. of

anode area, however, for most satisfactory opera- 5 tion, we prefer tooperate in the neighborhood of 27 to 30 amperes per sq. ft.

The electrolyte is a dilute solution containing sodium sulfate, disodiumphosphate and monosodium phosphate. we have obtained satisfac- 10 toryresults using a solution containing 4.5% of Na2SO4 and 0.5% of a mixtureof Na2HPO4 and NaHzPOr, the proportions of the latter two salts beingsuch as to give a pH between 5.0 and 8.0.

While the composition of the product is sub- 15 stantially' unchangedbetween these last enumerated pH values,-for most satisfactory operationwe prefer to operate withan electrolyte containing the above mentionedsalts, the sodium phosphates being therein proportioned so as to 20 givea pH between the limits of 6.0. to 6.4, whichelectrolyte it will berecognized issomewhat on the acid side of neutrality. During operationthe electrolyte tends to-become more basic, which condition is correctedby the regulated addition 25 of phosphoric acid to the-electrolyte,During operation the temperature of the electrolyte is maintained atapproximately 30 C.

' The product of our process is a double salt of tribasic copperphosphate and disodium phos- .phate. The formation of this compoundtherefore withdraws sodium phosphate from the electrolyte which compoundmust be replaced. We

' find it necessary to add disodium phosphate in addition 'to thephosphoric acid already men- 35 tioned to the electrolyte in' order tokeep the sodium phosphate contentof the electrolyte substantiallyconstant.

The formation of the copper phosphate-sodium phosphate complex occurs asa light blue, very finely divided precipitate in the electrolyte. For

continuous operation we therefore remove continuously a portion of theelectrolyte containing the suspended product, pass the same through afilter press and return the filtrate to the elec'- trolytic cell. Thefiltrate returned to the cell is caused to agitate the electrolyte toprevent the copper phosphate from settling out on the bottom. The filtercake in the press is washed, then removed from the press and dried. Itmay then be finely ground for use as a fungicide, or as an ingredientthereof.

The product as produced by our process has a composition correspondingto the formula:

neighborhood of 6. It is a light blue powder insoluble in cold water andwhen ground to a size suitable for use in fungicidal preparations it hasa particle size varying from 2 to microns. The bull: density variesbetween 10 and 15 lbs. per cubic foot and usually is in the neighborhoodof 12 to 13 lbs. per cubic foot. This is considerably less than thedensity of copper phosphate as produced by the reaction of' copper oxideand phosphoric acid the latter having been found to have a bulk densityof 50-53 lbs. per cubic foot when ground to thesame degree of finenessas the product produced by the present process.

The electrolytic product as herein prepared consists of agglomerates ofcrystals of the copper phosphate complex, over 99 per cent of the ag-'.crons 17% between and 12 microns and 20% The electrolytic less than 12microns in size.

" product as herein produced is. also distinguished from the productproduced by the reaction of copper oxide and phosphoric acid in that thelatter has bulk density approximately foultimes that of our product.

The copper phosphate-sodium phosphate complex as produced by our processnormally carried in the neighborhood of 6 molecules of water ofcrystallization. By heating the complex we are able to lower the amountof contained water of crystallization to any desired degree and indeedwe may make a susbtantially dehydrated product merely by heating to the,dehydrating tempera- 4o ture.

We may also produce .tribasic copper phosphate: C113(PO4)2 by leachingthe copper-sodium phosphate double salt with hot water. The sodiumphosphate may be removed in whole or in part. The tribasic copperphosphate thus produced is of low bulk density and may be used as aningredient of fungicides in the usual manner.

The sodium phosphate removed from the cupper a slurry with water, by theincorporation therewith of lime or colloidal clays. Other insecticidesor fungicides may be incorporated with the normal copper phosphate orwith the complex if desired. Our product being of extremely fineparticle size and of low density is particularly useful when employedwith the customary spreaders and adhesives Field experiments with ourimproved fungicide have indicated successful control .of the variousfungus diseases which attack peach and apple trees, with considerablyless damage to the plant than commercial Bordeaux mixture.

What we claim is:

1. The process for the electrolytic production of copper phosphatecomprising subjecting an aqueous electrolyte containing sodium sulphateand sodium phosphate and substantialy free of chloride and chlorateions, to the electrolytic action of a direct current in the presence ofa copper anode and removing copper phosphate from the-electrolyzedsolution.

2. The process for the electrolytic production of copper phospha/tecomprising subjecting an equeous, substantially chlorine-free,electrolyte containing sodium .sulphate andv sodium phosphate, andhaving a pH within the range of 5.0 to 8.0, to-the electrolytic actionof a direct current in the presence of a copper anode, and removing'copper phosphate from theelectrolyte.

3. The process for the electrolytic production of copper phosphatecomprising subjecting an aqueous electrolyte, substantially free ofchloride and chlorate ions and containing sodium sulphate and sodiumphosphate in dilute solutions, said solution having a pH within therange of 6.0 to 6.4 to the electrolytic action of a direct current inthe presence of a copper anode and removing copof copper phosphatecomprising subjecting an aqueous electrolyte substantially free ofchloride and chlorate ions and containing sodium sulphate and sodiumphosphate in dilute solution, said solution having a pH within the rangeof 5.0 to 8.0, to the electrolytic action of a direct current emperespersquare foot of anode area, and removingcopper phosphate from theelectrolyte.

5. The process for the preparation of copper phosphate comprisingsubjecting an aqueous electrolyte comprising a dilute solution of sodiumsulphate and sodium phosphate, said electrolyte being substantially freeof chloride and chlorate ions, to the electrolytic action of a directcurrent in the presence of a copper anode and maintainploying a copperanode in said electrolyte at a current density within the range of 15 toaming the pH of the electrolyte within the range of 5.0 to 8.0 by theaddition of phosphoric acid and sodium phosphate to said electrolyte.

CHARLES F. BOOTH. HERBERT J. KRASE.

